The three dimensional structure of DNA as influenced by base sequence, metal ions, chemical carcinogens and other agents will be studied by vacuum-ultraviolet circular dichroism (VUV-CD) and time resolved fluorescence. The electronic states and transitions of the DNA bases, understanding of which is crucial to the interpretation of CD spectra, will be studied using vacuum-ultraviolet magnetic circular dichroism (VUV-MCD) and fluorescence polarization spectroscopy. A major goal is understanding why VUV-CD is a better indicator of the helical structure of, and more sensitive to the hydrogen bonding between DNA strands than is conventional, longer wavelength CD. The VUV-CD, VUV-MCD, fluorescence polarization and time-resolved fluorescence experiments will be performed at the National Synchrotron Light Source.